ORIGINAL: jimk2
I think the C5 C6 is the most powerful .21 engine available. The Novarossi 421B is also awesome it has mega bottom end and insane power all the way through the power band. The JP FX21 is a lot calmer, It has a smooth powerband and is easier to control and ideal for tecnical tracks.
The point I'm making is somtimes you can have too much power, as it is harder to control.
you are a little off here. The 421B has insane TOP end, soft on the bottom compared to any P5 based engine. JP FX21's are powerhouses whether they are stock or mods.